In the processing of semiconductor devices, such as transistors, diodes and integrated circuits, a plurality of semiconductor devices are fabricated simultaneously on a thin slice of semiconductor material called semiconductor wafer. Such a semiconductor wafer is extremely brittle and easily contaminated. Thus, in the manufacturing of semiconductor integrated circuits, care should be taken to avoid physical damage and contamination to the semiconductor wafers.
Various known techniques enable the handling of wafers without human intervention. One known wafer handling device makes use of vacuum to hold the wafer in intimate contact with a pickup surface of the device. Such an intimate contact may result in possible damage to, and contamination of, the wafer.
Another known wafer pickup device is described in U.S. Pat. No. 3,341,009 issued on Mar. 4, 1969 to W. K. Mammel and assigned to the assignee herein. In such known pickup device, a semiconductor wafer is supported on a layer of fluid thus avoiding the above-discussed disadvantages of the intimate contact between a surface of the wafer and the surface of the pickup device. Although the device disclosed by W. K. Mammel operates satisfactorily for its intended purposes, retaining pins attached to the device and located around the peripheral edge of the wafer are required to limit the random lateral shifting of the wafer relative to the pickup surface. Any resulting frequent impacts of the edge portion of the wafer against the pins may cause the generation of particles leading to physical damage, contamination, and ultimately low yield of the integrated circuits produced. Furthermore, the retaining pins, outwardly protruding around the edge of the wafer, prevent such known device from reaching into a wafer cassette between adjacent wafers and picking up a predetermined wafer.
Therefore, there exists a need for a technique for handling semiconductor wafers while substantially minimizing the deleterious effects of wafer contamination, and enabling the loading/unloading of wafers into/out of wafer cassettes.